1. Field of the Invention
The present invention generally relates to a method of tuning transformers with resistive and capacitive loads connected to the transformer to resonate at some given frequency and, more particularly, to an automated method for tuning a transformer to produce a resonant circuit in order to match elements within an acoustic array to transceiver electronics.
2. Description of the Prior Art
The tuning of transformers is useful for several applications. Tuning is done to produce a resonant circuit where the phase angles of the resulting current and the applied voltage are the same, that is, they are in phase. As used in the specific application described herein, the resonant circuit is produced between the reactive load created by a resistor and a capacitor and the transformer to be tuned. To tune a transformer using conventional methods, the values of capacitance and resistance are selected and connected to the transformer as shown in FIG. 1. In FIG. 1, the transformer 10 to be tuned has a primary winding 11 and a secondary winding 12. The secondary winding 12 has a plurality of reactive loads 13, 14 and 15 connected to it. These loads are represented by a resistor R.sub.o and a capacitor C.sub.o connected in parallel and may be connected across the entire winding of the secondary as indicated by load 13 or across intermediate taps of the secondary as indicated by loads 14 and 15. A signal generator 16 supplies a signal at the desired resonant frequency to amplifier 17 which drives the primary winding 11 of the transformer. An oscilloscope 18 having voltage and current inputs is connected in the primary circuit of the transformer. Specifically, the voltage inputs are connected across the primary winding 11, and the current inputs are connected to a current transformer 19. The core of the transformer was then moved until the circuit was purely resistive and the phase angle was zero degrees as indicated by a lissajous pattern on the oscilloscope 18. Alternatively, the phase angle could be measured by another phase sensitive device.
Also known in the prior art are methods of measuring impedance or calculating impedance knowing voltages and currents. For example, U.S. Pat. No. 4,342,089 to Hall describes impedance measurement calculations using a computer or a calculator. If the unknown impedance is Zx, Hall's method measures the voltage across Zx and across a range resistor Rs. This measurement is phase sensitive and provides the quadrature components needed to calculate the capacitance and inductance knowing the frequency. While this is a method to measure impedance, it is not related to the resonant adjustment of transformers using a computer.
Huang et al in U.S. Pat. No. 4,246,535 describe a method of design of a linear radio frequency amplifier. This method applies two signals of different frequencies to the circuit and then varies the impedance at the output while determining the output power of the amplifier for a family of load impedances. This patent goes on to describe a method to determine the desired linearity and maximum output power of the amplifier; however, Huang et al are not concerned with the tuning of transformers.
U.S. Pat. No. 4,404,636 to Campbell, Jr. et al describes a test set for measuring the phasor impedance of a circuit under test. The test set produces a frequency from a signal generator for application to the circuit being measured. The test set then measures the resistance and reactance components of the measured impedance. A microprocessor calculates the magnitude and phase of the impedance. While the Campbell, Jr. et al test set measures impedance, it is not used for the resonant adjustment of transformers.
U.S. Pat. No. 4,497,030 to Bowling et al describes a computer aided characterization of symmetrical N-way microwave power combining structures.
U.S. Pat. No. 3,082,373 to Hooke et al describes a method to adjust an alternating current bridge, specifically a Wien bridge, to obtain a null output in the shortest time possible. The Hooke et al procedure is specifically intended for the measurement of capacitors.
U.S. Pat. No. 3,319,162 to Sattinger also describes a method for measuring impedances. This is performed by a system similar to a conventional impedance bridge; however, the bridge is not nulled, and the magnitude of the voltage is used as a measure of the reactance of the circuit component.
U.S. Pat. No. 3,441,726 to Honore et al describes a method using a computer and passive devices to produce a circuit that appears as a variable impedance or admittance that is controllable. The variable impedance might be used as a model in, for example, an analog computer; however, the Honore et al method does not involve resonant tuning of a transformer by the use of a computer model.
U.S. Defensive Publication No. T940,013 to Ho describes the use of a computer to perform direct current or transient analysis on a network. Ho does not use any instruments to perform measurements on a physical device. Rather, Ho describes software modeling.
U.S. Pat. No. 4,300,196 to Lopresti describes the use of a computer to adjust circuit components. The computer is used as a feedback mechanism to adjust machine adjustable components within a circuit. The computer monitors the results of the adjusted components to produce new values that are used to adjust other adjustable components. Lopresti's method does not, however, cover the modeling and adjustment of transformers in a resonant circuit.
Thus, while the prior art generally discloses various methods of automated measurement of impedance values and even the adjustment of impedance values, there has not heretofore been known a satisfactory automated method for tuning a transformer to produce a resonant circuit in order to match elements wherein the phase angle of the resulting current and the applied voltage is in phase. While manual methods are known and suffice for the tuning of a single transformer, the problem of manually tuning an array of transformers, such as used for example in an acoustic array, becomes increasingly difficult to accomplish as the size of the array increases.